Soil with the spores of fungi in dormant stage from previous years infections belonging to the genus Fusarium caused significant loss of onion yield in Poland. The most important form of Fusarium inoculum in the field are chlamydospores, which may survive in soil for many years. There are no available methods to eradicate chlamydospores from soil environment. Inspired by data from the literature and own prelimi–nary observation, we evaluated the effect of application of Brassicaceae plant material to the soil infested with F. oxysporum and F. solani isolates, which are pathogenic to onion. Obtained results showed that addition of fresh plant material from B. juncea and B. alba had no effect on amount of Fusarium propagules in the soil. Moreover amendment of infested soil with dry plants or milled seeds of B. juncea or B. nigra significantly stimulated the population of Fusarium in the soil.